1. Field of the Invention
The present invention relates to a stator and DC brushless motors including the stator and, more particularly, to a stator without silicon steel plates and DC brushless motors including the stator.
2. Description of the Related Art
Currently available DC brushless motors include an outer rotor type and an inner rotor type. Outer rotor type motors have advantages of simple structure, good heat dissipation, and low costs, whereas inner rotor type motors have better rotational stability.
FIGS. 1 and 2 show a conventional outer rotor type motor 8 including a base 81, a stator 82, and a rotor 83. The base 81 includes a shaft tube 811. The stator 82 is mounted to an outer periphery of the shaft tube 811. The rotor 83 includes a permanent magnet 831 and is rotatably extended through the shaft tube 811. More specifically, the stator 82 of the motor 8 includes a plurality of silicon steel plates 821, an upper insulating sleeve 822, a lower insulating sleeve 823, and a coil unit 824. The silicon steel plates 821 are stacked up and engaged with each other as a single member. The upper and lower insulating sleeves 822 and 823 are coupled to two ends of the stacked silicon steel plates 821. The coil unit 824 is wound around the silicon steel plates 821 and the upper and lower insulating sleeves 822 and 823 at predetermined portions.
The silicon steel plates 821 are formed by pressing and then stacking one upon another. Next, the upper and lower insulating sleeves 822 and 823 are respectively coupled to the ends of the stacked silicon steel plates 821 before winding the coil unit 824. The stator 82 has many components and, thus, a complicated structure, resulting in high manufacturing costs and assembling inconvenience. Furthermore, the axial height of the stator 82 is relatively large, such that the overall volume and the overall axial height of the outer rotor type motor 8 can not be effectively reduced. As a result, miniaturization of the outer rotor type motor 8 is almost impossible. Further, the permanent magnet 831 of the rotor 83 includes a plurality of alternately disposed north poles and south poles. Torque change or uneven torque (also known as cogging torque) occurs when the north and south poles of the permanent magnet 831 move relative to magnetic pole faces formed by the silicon steel plates 821 of the stator 82. Vibration easily occurs especially when the rotor 83 rotates at low speeds.
FIGS. 3 and 4 show an inner rotor type motor 9 including a housing 91, a stator 92, a rotor 93, and a permanent magnet 94. The housing 91 is hollow and receives the stator 92. The rotor 93 includes a shaft 931 rotatably received in the housing 91 and extending through the stator 92. The stator 92 interacts with the permanent magnet 94 to drive the rotor 93 to rotate. The stator 92 of the inner rotor type motor 9 also includes a plurality of silicon steel plates 921, upper and lower insulating sleeves 922 and 923, and a coil unit 924. The stator 92 of the inner rotor type motor 9 is substantially the same as the stator 82 of the outer rotor type motor 8 and, thus, has the same disadvantages including high manufacturing costs, assembling inconvenience, difficulties in reducing the axial height, and low rotational stability.